Magick cannot do physical changes. With weight, its more of a placebo, or perhaps speeds result, but either way you need to do the work. What exactly are you wishing to gain? Fat or muscle? Look into high protein and weights if its muscle mass. if its weight gain in your legs focus on building muscle in that area [squats for instance] rest for a day, and slowly increase weight or repetition of exercise. Fat, while not as healthy, try to increase your calories. Don't eliminate exercise, just make sure your calorie intake is more than calories burned. Example, if you usually require 1500 calories in a day, try having 2000. Either way, speak with your doctor for a healthy weight gain plan.

No such spells exists. If it's muscle go lift weights or eat a healthy diet. A spell might be able to move the process along, but it won't make it happen. If you're working on gaining fat, then eat fast food everyday, cakes, brownies, and other junk food, eat to much of it. Also to gain muscle weight, do about 50 push-ups and sit-ups in the morning and evening. Run a lot. Rode a bike. Buy exercise tools. Just get physically fit is basically what I'm saying for muscles. For fat eat non-healthy food. Also sit around the entire day, and do nothing to burn the fat away. This is my advice for each type of weight gain muscle and fat.